The invention relates to controlling the setup or continuation of a call charged from a prepaid group account, particularly when there are at least two ongoing calls charged from the prepaid group account.
In a prepaid service, each prepaid subscription has its own account, the balance of which is reduced during an ongoing call charged from the subscription. In solutions based on an intelligent network, a prepaid subscription is charged in phases and usually at least two network nodes participate in the charging. The balance of the account is monitored in the service control point (SCP), which comprises a current credit, i.e. the maximum amount of money on the account, and a reserved credit, which is the amount of money reserved from the current credit for this call for a certain period of time. The amount of the reserved credit depends on a threshold, which is a network parameter usually expressed as time, and on a price of one time unit for this call. The SCP sends the threshold to the service switching point (SSP). The service switching point is a call monitoring network node, for example a mobile switching centre. When the time indicated by the threshold has elapsed, the SSP reports this to the SCP and at the same time requests another threshold. In response to receiving the report, the SCP updates the current credit by deducting from the current credit the reserved credit. The SCP updates also the reserved credit similarly. After this updating, the SCP checks if the current credit minus the reserved credit exceeds zero. (The outcome can also be called a temporary balance.) If so, a new threshold is given to the SSP for this call and the reserved credit is updated. Otherwise the SCP instructs to release the call. If the user of the subscription releases the call before the threshold elapses, the SSP reports the time used to the SCP. In that case the SCP updates the current credit by deducting from the current credit the cost of the time used and the reserved credit is updated by deducting from it the reserved credit (i.e. the cost of the threshold).
The prepaid subscription can also be a prepaid group subscription, where subscribers belonging to a group share one common prepaid subscription account. In that case there is one current credit and each ongoing call reserves its own credit portion from the current credit, and the reserved credit is the sum of reserved credit portions for ongoing calls. When there are more than one ongoing calls charged from the subscription account, there is a risk of a call requesting a new threshold being released because the current credit minus the reserved credit is zero, although, for example, one second later an ongoing call is released before it has used its threshold. In other words, after that latter call is released, the current credit minus the reserved credit exceeds zero and the first call release was performed in vain. It is also possible that when there are other ongoing calls, a subscriber wanting to make a call does not succeed because the current credit minus the reserved credit is (temporarily) zero. This can happen to any group regardless of its size or the amount of the current credit, since any number of calls charged from the group account can be made simultaneously.
One way to minimize the problem is to use small thresholds. This solution, however, increases signalling between the SSP and the SCP, and thus also the load on the SSP and SCP, especially when the subscribers are roaming.
An object of the invention is to provide a method and an apparatus implementing the method to minimize the above-mentioned problem. The objects are achieved with a method and a network node which are characterized in what is disclosed in the independent claims. The preferred embodiment of the invention are set forth in the dependent claims.
The invention is based on realizing the problem and minimizing it by determining a negative limit for the group subscription. The negative limit is determined on the basis of at least one parameter. Thus the negative limits for different groups may differ. It is even possible that the negative limit for one group varies over time or there are different negative limits for different kinds of group members. The negative limit indicates how much the account balance can be below the preset minimum balance. Consequently, the negative limit can also be called an undercut. The most important advantage of the invention is that a risk for an improper call release is minimized, and, with the use of at least one parameter, the possible losses to a service provider can also be minimized.